fix: keep System.dat lines whose values agree

The rom line renderer upper-cased every crc, so Dinothawr.zip's
683ed4ad, the one lower-case crc libretro writes, changed with no
correction behind it. A line whose values match ours now keeps its
bytes, a corrected crc follows the case of its own line, and an added
line keeps the file's upper case. An empty truth hands System.dat back
byte for byte for RetroArch and Lakka.

scripts/exporter/systemdat_exporter.py

@@ -42,6 +42,26 @@ def _quote(name: str, quoted: frozenset[str] = frozenset()) -> str:
 _ROM_NAME = re.compile(r'^(\s+)rom \( name ("[^"]+"|\S+)')
 
 
+_CRC = re.compile(r" crc (\S+)")
+
+
+def _patch(line: str, indent: str, ours: str) -> str:
+    """The original line where our values agree with it, else ours in its form.
+
+    libretro writes one crc in lower case (Dinothawr.zip's 683ed4ad) and the
+    others in upper case. A line whose values did not change keeps its bytes,
+    and a corrected crc takes the case of the line it lands on. The
+    indentation stays libretro's.
+    """
+    ours = indent + ours.lstrip("\t")
+    if line.lower() == ours.lower():
+        return line
+    theirs = _CRC.search(line)
+    if theirs and theirs.group(1) != theirs.group(1).upper():
+        ours = _CRC.sub(lambda m: f" crc {m.group(1).lower()}", ours, count=1)
+    return ours
+
+
 def _sections(original: str) -> list[tuple[str, list[str]]]:
     """The system sections of a System.dat, each comment with its rom lines."""
     _, sep, body = original.partition("\ngame (")
@@ -191,8 +211,7 @@ class Exporter(BaseExporter):
             for line in roms:
                 match = _ROM_NAME.match(line)
                 if match and match.group(2) in rendered:
-                    # The values are ours, the indentation stays libretro's.
-                    body.append(match.group(1) + rendered.pop(match.group(2)).lstrip("\t"))
+                    body.append(_patch(line, match.group(1), rendered.pop(match.group(2))))
                 else:
                     body.append(line)
             body.extend(rendered.values())